<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>transfrom左右居中</title>
  <style>
    .box {
      width: 200px;
      height: 200px;
      background-color: #000;
    }

    .box1 {
      position: relative;
      left: 50%;
      transform: translateX(-50%);
    }
  </style>
</head>

<body>
  <div class="box box1"></div>
</body>

</html>